You find yourself in an airport or hotel room in another country, and you really need to charge your phone, camera or game system. But what is that strange-looking outlet? It has round holes! And there are two? Or three? What is going on here? Why does this country not use the same plugs that I use back home?
The short answer is that the systems that deliver electricity to homes around the world have been built by thousands of people over the last 140 years. And they are not finished yet. Around the world, about 750 million people – one out of every 10 – still do not have access to electricity. But for the 90% who do, there are 15 different types of domestic electrical outlet plugs in use around the globe.
To understand why electric outlets are not all the same, you…